There are several occasions when access devices, such as needles or catheters or the like, are inserted into a patient. The purpose is often to deliver a liquid to the patient. This liquid may be a saline solution that helps restore the fluid balance of the patient, a glucose solution or other nutritional supplements or a solution containing a drug that should be delivered continuously. It may then be important to make sure that the needles are not unintentionally withdrawn from the patient, especially if this state remains undetected.
Other cases when access devices are regularly inserted into a patient are in blood cleaning treatments such as hemodialysis, hemofiltration, hemodiafiltration or plasmafiltration. For people who have lost all or most of their kidney function, it is necessary to find alternative ways of cleaning the blood. One option is to have a new kidney transplanted. Due to the limited availability of organs, the immunological demands on matching between organ and recipient and a number of other reasons, this possibility is only open to some patients.
One alternative to transplantation is dialysis, which has to be performed at regular intervals, usually several times per week, and takes a few hours each time. In dialysis the waste products in the blood are transported across a membrane to a cleaning fluid. In hemodialysis, the most common form of dialysis, blood is removed from the patients body and pumped into an extracorporeal fluid circuit by means of a blood pump. The extracorporeal fluid circuit includes an external device, a dialyser. The dialyser contains a membrane where blood is flowing on one side and a dialysis fluid is flowing on the other side whereby the blood is purified by means of dialysis. The purified blood is then returned to the body. The blood is usually removed from and returned to the body via access devices in the form of hollow needles, which are preferably inserted into a blood vessel in the lower part of one arm. However also other locations for insertion of the needles are possible. In order to facilitate a frequent access to the blood vessel, and also to increase the available flow of blood in that vessel, it is a common practice to create a so-called arterio-venous fistula. Connecting a suitable artery directly to a vein by a surgical procedure creates the fistula. Another possibility is to surgically insert an artificial vessel, i.e. graft, in between an artery and a vein, which graft is then used for the insertion of the needles. Hereinafter the expression vessel will be used while it is understood that the expression vessel comprises blood vessel as well as artificial vessel, graft, fistula and other types of vessels for use in the herein disclosed technical field.
In either case it is, thus, required to insert access devices into the vessel of the patient, each time a dialysis treatment is to be performed. It is then of utmost importance that the access devices are not unintentionally withdrawn during the treatment. If the arterial access device (the one where blood is removed from the patient) is unintentionally withdrawn without being detected, the blood already in the extracorporeal fluid circuit may continue to be pumped by the blood pump. If the venous access device (the one where the blood is returned to the patient) is still in place the blood will then be returned from the extracorporeal fluid circuit to the patient. When all the blood has been returned to the patient by means of the blood pump and if the blood pump is still in operation, air will be pumped into the patient. This would be potentially harmful to the patient and has to be prevented. If, on the other hand, the venous access device would be unintentionally withdrawn without being noticed, all the blood that should have been returned to the patient will instead be lost to the surrounding area. This may be fatal to the patient already after a few minutes, and should therefore be prevented. If both access devices are withdrawn at the same time, no harmful situation will normally arise, although the blood present in the extracorporeal circuit will be lost. However, if this situation remains undetected for a long time, treatment time is lost.
To prevent unintentional withdrawal of access devices it is normal practice in dialysis machines to measure the pressure in an external tubing, constituting the extracorporeal fluid circuit, upstream of the venous access device. This pressure is usually measured in a drip chamber attached to the dialysis machine. The pressure is measured by means of a pressure sensor. For the detection of unintentional withdrawal of the venous access device from the vessel, any alarm must be connected to tightly limited intervals of acceptable changes of the venous pressure. A problem with this technique is that the pressure at the site of the pressure sensor is a result of static pressures due to a height difference between the drip chamber where the pressure is measured and the tip of the access device where the pressure in the vessel is measured and the pressure drop due to the flow of blood in the external tubing. It may therefore happen that changes in the height difference of the venous access device and the changed flow resistance when the access device is withdrawn counteract each other so that the resulting pressure change is too limited to be detected, i.e. the changes of the venous pressure is kept within the accepted interval. An unintentionally withdrawn venous access device may lead to fatal results for the patient.
There is, thus, a need for devices that may increase the safety against unintentional withdrawal of any access device during dialysis, and a number of methods have been suggested. The suggested methods may be divided in two different classes. One class of methods aims at detecting when any access device is withdrawn in order to give an alarm to the user. The other class of methods aims at physically preventing the withdrawal of any access device.
Detection of withdrawal of any access device may be made e.g. by use of a reed-relay fixed to the skin which can detect the movement of a magnet mounted in the blood tube as suggested in U.S. Pat. No. 5,578,003. Another possibility is to attach fluid sensing devices, e.g. based on measurement of electrical conductivity, on the skin around the access devices, which is suggested in the PCT application WO 99/24145.
These methods do not prevent the withdrawal of access devices, and manual intervention, as a result of the emission of an alarm signal, is therefore needed to avoid a fatal outcome.
Safer in this respect are the devices that aim at preventing the withdrawal of the access devices. Such devices are e.g. disclosed in U.S. Pat. Nos. 3,900,026, 5,084,026, 5,112,313 and 5,449,349. They all describe devices that are attached to the patients skin, either by tape or by straps around the arm, and to which a single access device may be secured. For dialysis two such devices are needed, one for each access device. It is time consuming to secure each access device in this way.
An alternative solution is provided by the device described in U.S. Pat. Nos. 5,911,706, 5,954,691 and 6,013,058 and in PCT applications WO 00/16834, WO 00/16844, WO 00/40282 and WO 00/53245. This device is implanted surgically under the skin, and is brought in permanent connection with the vessel using two access devices, one for extracting blood and one for returning blood, which are also in their entire length located within the patient's body. Each time that a dialysis procedure is to be performed access is gained to the vessel by inserting two access devices in parallel through the skin of the patient and into specially designed ports in the implanted device. These ports are so designed as to close off the access to the vessel when no access devices are inserted. The device is further designed to lock the access devices in their position when they are inserted into the device in order to prevent unintentional withdrawal of the access devices. As a further safety measure, both access devices are linked together so that if one of the access devices would be unintentionally withdrawn despite the locking mechanism, the other access device would also be withdrawn. The device requires a surgical procedure for its insertion. Due to immunological and other mechanisms in the human body, such implanted devices have a very limited lifespan in the body. It is therefore a short-term solution for the blood access to dialysis patients. It is quite a costly device compared to the use of ordinary dialysis access devices.
WO 01/03754 discloses an insertion guide for inserting an arterial access device and a venous access device, respectively, into a vessel in the form of a fistula. The insertion guide guides the respective access device into the fistula. The access devices are secured in their inserted position by means of a latching piece, which is connected to the respective access device and arranged in a recessed channel and locked in position by means of a clamping screw. This device is limited with respect to how, e.g. in respect of choice of directions, access devices may be arranged in the fistula. This device is complicated from the point of view of avoiding unintentional withdrawal of any access device.